Inkjet printers have been widely used as digital signal output equipment in general homes because of having advantages such as low noise, low running cost, and easiness of color printing.
In recent years, inkjet techniques have been increasingly utilized not only in such homes but also for industrial applications such as a display, a poster, and a bulletin board.
In such applications, since porous mediums are problematic in terms of durability such as lightfastness, water resistance, and wear resistance, non-porous recording mediums such as a plastic film have been used, and inks therefor have been developed.
As such inks, for example, solvent-based inkjet inks using an organic solvent as a vehicle, and ultraviolet curable inkjet inks including a polymerizable monomer as a main component have been ever used widely.
However, the solvent-based inkjet inks are not preferable in terms of environmental load because the solvent is evaporated in the atmosphere, and the ultraviolet curable inkjet inks have limited application fields because they may have skin sensitizing properties depending on the monomer to be used and an expensive ultraviolet irradiation apparatus is required to be incorporated to the main body of a printer.
In view of such background, there have been recently developed inkjet inks capable of being directly used for printing on a non-porous substrate, which are aqueous inks for inkjet recording which give less environmental load and which have been widely used as inkjet inks for household use. Examples of such attempts can be found in PTL 1 and PTL 2.
However, such aqueous inks generally have several drawbacks pointed out in terms of image quality, as compared with the solvent-based inkjet inks.
First, while the inks must be immediately dried on a non-porous substrate because of not essentially penetrating into the substrate, water itself which is the main solvent of the aqueous ink, and a water-soluble organic solvent added as an additive tend to cause deterioration in drying properties to result in poor drying, and therefore ink show-through, so-called blocking, may occur when printed articles are stacked or rolled up.
In addition, while the non-porous substrate is very glossy in many cases and thus there are demanded for inks which achieve high gloss so that a sense of unity between a printed portion and an unprinted portion as a recorded product is not impaired after printing, particles are fused to form a coating film unlike the case of the solvent-based inks into which a resin is dissolved, and thus the surface is easily roughened and the gloss thereon is easily impaired.